Latching reciprocal ferrite phase shifter having mode suppressing means



Get. 7, 1969 J. K. PARKS ET AL 3,471,809

LATCHING RECIPROCAL FERRITE PHASE SHIFTER HAVING MODE SUPPRESSING MEANS Filed Feb. 28, 1968 2 Sheets-Sheet 1 FIG MODE S UPPRESSOI'? FERR/ TE F 2. JOE K PA/Qk BRUCE R. SAVAGE ATTORNEY Oct. 7, 1969 J. K. PARKS ET AL 3,471,809

LATCHING RECIPROCAL FERRITE PHASE SHIFTER HAVING MODE SUPPRESSING MEANS Filed Feb. 28, 1968 2 Sheets-Sheet RES] DUA L MAGNETIZATION- RESET CONDITION 22 31 31 21 3 23 M i DRIVER f; k L-,

A i 2: 1] llfl/ZQ 1:: 26 It 4 5 27 Ill I 4 III DRIVER K 3 l l 1 ]28 25 RESIDUAL MAGNETlZATlON-SET CONDITION JOE K. PAR/(5 BYBRUCE SAVAGE ATTORNEY 3,471 809 LATCHlNG RECHPROCAL FERRlTE PHASE SHIFTER HAVHNG MODE SUPPRESSlNG MEANS late if. Parks and Bruce R. Savage, Clearwater, Fla, as-

signors to Sperry Rand Corporation, a corporation of Delaware Filed Feb. 28, 1968, Ser. No. 763,959

Int. Cl. HtlSh 7/30 US. Cl. 33331 6 Claims ABSTRACT OF THE DISCLOSURE A phase shifter comprising a ferrite plate having two rectangular slots and being positioned longitudinally inside a reduced height rectangular waveguide. The slot-ted ferrite plate constitutes a three-arm toroid, the side arms of which extend toward the narrow walls of the waveguide and have a cross-sectional area equal to half that of the center arm. One pair of pulsed coils on the side arms magnetizes and latches the center arm in accordance with the magnitude of coil current. A second pair of pulsed coils on the side arms demagnetizes the center arm. Mode suppressors isolate the side arms and the coils from the microwave interaction region of the center arm.

Background of the invention The invention relates to phase shifters of the Reggia- Spencer type wherein a magnetized ferrite member within a rectangular waveguide introduces an amount of phase shift in microwave energy travelling in either direction in accordance with the magnitude of the magnetizing field. In a typical prior art form of the Reggie-Spencer device, a ferrite rod is centrally located in a rectangular waveguide and magnetized longitudinally by current flowing in a coil placed outside the waveguide. The longitudinally magnetized ferrite rod produces large phase shift variations as a function of magnetizing field if the rod diameter is greater than a critical amount which provides adequate field concentration within the rod. Only moderate success, however, has been achieved so far in an efiort to develop a latching phase shifter of the aforementioned reciprocal type. One or more of the following problems have not heretofore been adequately overcome: high loss, large VSWR and insertion loss variations, non-linear phase versus frequency response, and higher order moding.

Summary of the invention The present invention provides an improved reciprocal ferrite phase shifter which may be latched to a maximum remanent state for maximum reciprocal phase shift or to a number of lesser remanent states, on respective minor hysteresis loops, in accordance with the magnitude of applied current. In a typical embodiment, the reciprocal ferrite phase shifter may be latched to settings which provide 45 phase shift increments between and 360. The latching currents are applied to coils mounted about the side arms of a three-arm apertured ferrite plate positioned longitudinally inside a reduced height rectangular waveguide. The internal magnetic domain structure in the center toroid arm vectorially sums to give an eifective longitudinal magnetization in the center arm having a magnitude dependent upon the amount of current applied to the side arm coils. A pair of L-shaped mode suppressors pass through respective slots and contact the inside and bottom surfaces of the side arms of the toroid. Each mode suppressor extends from one broad wall of the waveguide substantially to the opposite wall where a thin dielectric strip separates the mode suppressor from the facing waveguide wall. The mode suppressors reduce the ole States Patent 0 3,471,809 Patented Oct. 7, 1969 effective waveguide width to prevent undesirable higher order modes and isolate the outer arms and the coils thereon from the active microwave region adjacent the center arm. Although each mode suppressor electrically contacts one of the broad walls of the rectangular waveguide, it is insulated from the other broad wall by the aforementioned thin dielectric strips to eliminate shortedturn effects which otherwise would be introduced and greatly hinder the switching of the phase shifter. The invention may be embodied in two terminal (transmission) or single terminal (reflective) rectangular waveguide devices.

Brief description of the drawings FIGURE 1 is a perspective view of a partly disassembled embodiment of the invention;

FIGURE 2 is a cross-sectional view of the embodiment of FIGURE 1;

FIGURE 3 is a series of hysteresis loop plots useful in understanding the operation of the embodiment of FIG- URE 1; and

FIGURE 4 is a schematic diagram of the embodiment of FIGURES 1 and 2 and the means for establishing maguetizations therein.

Description of the preferred embodiment Referring to FIGURE 1, ferrite plate 1 is provided with rectangular slots 2 and 3 and is placed longitudinally within reduced height rectangular waveguide 4 in a position parallel to the broad walls of waveguide 4. Slotted ferrite plate 1 consists of side arms 5 and 6 and center arm 7. Side arms 5 and 6 extend toward the narrow walls of waveguide 4. The cross-sectional areas of side arms 5 and 6 are one-half that of the center arm 7 in order to sustain a remanent flux level in the center arm equal to the sum of the side arm flux contributions. Dielectric matching steps 19 and 20 match the phase shifter into reduced height waveguide.

As shown more clearly in FIGURE 2, conductive L-shaped mode suppressors 8 and 9 are positioned ad jacent the inside Walls 10 and 11 of side arms 6 and 5, respectively, of the ferrite toroid. The surfaces 12 and 13 of mode suppressors 8 and 9 electrically contact the broad wall 14 of rectangular waveguide 4. The opposing broad wall 15 of waveguide 4 is electrically insulated from mode suppressors 8 and 9 'by thin dielectric strips 16 and 17. Coils 18 are wound about side arms 5 and 6 for latching the center arm 7 in a number of controllable remanent flux level conditions in accordance with the magnitude of applied current pulses. Mode suppressors 8 and 9 are slotted to allow space for coils 18 where they are wound about side arms 5 and 6. The mode suppressors 8 and 9 permit the use of a continuous magnetic circuit in the toroid for large figure of merit (phase shift per unit loss) while still isolating the side arms of the toroid and the wires wound thereon from the microwave energy propagating through the central active microwave region. In addition, the mode suppressors reduce the effective width of rectangular waveguide 4 and eliminate undesirable higher order modes within the waveguide. The thin dielectric strips 16 and 17 disrupt the conductive DC loop that would otherwise be formed by each of the mode suppressors and the adjacent waveguide walls thereby reducing the so-called shorted-turn effect and improving switching characteristics. The capacitors formed by the dielectric strips and the contiguous mode suppressor and waveguide surfaces are of sufiicient size to complete the RF. path introducing objeotional reactance.

The dimensions of a typical 15.8 gigahertz design of the present invention are shown in FIGURE 2. It was found that increasing the lateral dimension of the central arm beyond 0.170 inch reduces the upper frequency limit of the phase shifter because of higher order moding. It was also found that increasing the lateral dimension of the side arms to facilitate a high remanent flux level in the central arm permits the propagation of microwave energy in the diele-ctrically loaded waveguides formed by the toroid side arms in combination with the mode suppressors and the narrow walls of waveguide 4. A relatively narrow side arm is essential to prevent the leakage of energy to the side regions and to restrict microwave energy propagation to the central region of the device.

As compared to a larger gap a small gap between the ferrite central arm and each of the waveguide broad Walls reduces insertion loss variations. However, the elimination of the gaps or the loading of the gaps (even With low dielectric constant materials) sharply reduces the amount of phase shift produced by the device. A gap of 0.015 inch affects an optimum compromise between high phase shift and low loss in the embodiment shown in FIGURE 2. The size of the central toroid arm plus the gap spacing results in a waveguide height of 0.160 inch. It also was found that the residual non-reciprocal component of phase shift due to lack of perfect structural symmetry of the phase shifter about the longitudinal axis of the waveguide can be significantly reduced by providing a very sharp curvature on the center arm of the toroid as shown at points 31 in FIGURE 4.

Current pulses applied to coils 18 surrounding the side arms 5 and 6 latch the center arm 7 into rernanent magnetic states as shown in the representative plots of FIG- URE 3. Remanent position +1 lies on the major hysteresis loop of the ferrite material and represents the maximum remanent magnetization which is obtainable in center arm of the toroid. Perturbation theory predicts that the phase shift of a ferrite slab centrally located in a rectangular waveguide is proportional to the phase constant [3 of the dielectrically loaded waveguide and the change in permeability A;/.. Since [3 and A are independent of the direction of microwave energy propagation in the case of the given geometry, the resultant phase shift is proportional to the magnitude of the applied magnetic field but is insensitive to the direction of the applied field. Thus, a reversal in the direction of the current pulse applied to coils 18 to produce remanent position +1 would latch the center arm of the toroid into remanent position 1 but would produce the same resultant phase shift. Lesser amounts of current applied to coils 18 produce reduced rem-anent magnetizations represented by positions :2, :3, and :4. It will be understood that the number of minor hysteresis loops depicted in FIGURE 3 is illustrative only. Larger or smaller numbers of minor loops can be achieved by adjustment of the number of increments of current applied to coils 18 to vary the phase shift between the minimum and maximum values obtainable.

The manner in which the phase shifter of the present invention is driven to desired latched positions can be seen by referring to FIGURE 4. In the preferred embodiment, two separate current driver circuits are provided, one each for the set and reset current pulses. One of the driver circuits receive-s trigger pulses of adjusta'ble amplitude at terminal 21 which is applied to driver 22 to provide current pulses through serially connected driver c-oil windings 23 and 24. The other driver circuit receives trigger pulses at terminal 25 of a predetermined amplitude which is applied to driver 26 to provide current pulses through series-connected driver coil windings 27 and 28.

Windings 27 and 28 are poled about respective side arms so that the resulting flux is oriented in the same direction around the perimeter of the toroid as represented by dashed arrow 29. Inasmuch as the two side arms are equally magnetically saturated by the predetermined amplitude pulses applied to terminal 25, there is no appreciable flux in the center arm. This flux condition may be termed the reset or non-magnetized state of the fer-rite. Windings 23 and 24 are identical to windings 27 and 28 except that the former windings are poled about respective side arms in senses which cause the resulting flux in the side arms to be opposed relative to one another around the perimeter of the toroid. As a result, a relatively strong magnetization is established in the center arm equal to the sum of the fluxes in the two side arms as represented by dashed arrow 30. This flux condition may be described as the set or magnetized state. As previously stated, the phase shifter of the present invention may .be operated at intermediate degrees of flux excitation in order to achieve incremental values of phase shift. This action is obtained by varying the amplitude 'of the set pulses applied to terminal 21 to achieve the desired incremental phase shift values. Using the embodiment of FIGURES 1 and 2, incremental phase shifts of from 0 to a full 360 were obtained at microwave frequencies of about 15.8 giga'hertz. The value of 0 is defined as the amount of phase shift produced in the reset condition. Linear phase versus frequency response was obtained when the frequency of the microwave energy was varied.

Although the embodiment of the present invention as shown in the drawing is a two-terminal (transmission) device, it can be readily modified into a single terminal (reflective) device by placing a short-circuit termination at one end of the three-arm toroid and making the toroid one-half as long as in the disclosed two-terminal case for the same amount of phase shift. Inasmuch as the device is reciprocal in phase shift operation, the propagating microwave energy experiences an equal amount of phase shift of the same sense for both directions of propagation through the single terminal device. The single terminal embodiment of the invention possesses the added advantages of lower cost, reduced size and ease of fabrication.

It will be recognized by those skilled in the art that the present invention utilizes the property of ferrites of being magnetically polarized material exhibiting the gyromagnetic effect within the frequency range of interest. It is in this sense that the term gyromagnetic material is employed in the appended claims rather than the metallurgically restricted term ferrite.

We claim:

1. A reciprocal phase shifter comprising:

a rectangular Waveguide,

a plate of gyromagnetic material having two apertures defining a three-arm toroid,

said toroid having a pair of side arms symmetrically disposed about a center arm,

said toroid being positioned longitudinally inside said waveguide so that said side arm's extend toward the narrow walls of said waveguide,

a pair of mode suppressors passing through respective ones of said apertures and extending from one broad wall of said waveguide substantially to the other broad wall thereof,

a dielectric strip separating each said mode suppressor from said other broad wall of said waveguide, and

means coupled to said side arms for producing magnetizations therein.

2. Apparatus as defined in claim 1 wherein said means coupled to said side arms produces substantially equal magnetizations therein of senses mutually aiding in said center arm.

3. Apparatus as defined in claim 1 wherein said means coupled to said side arms produces substantially equal magnetizations therein of senses mutually opposed in said center arm.

4. Apparatus as defined in claim 1 wherein said means coupled to said side arms comprises:

a first pair of series-connected coil windings wound about respective side arms to produce flux oriented in the same direction around the perimeter of said toroid,

a second pair of series-connected coil windings wound about respective side arms to produce flux oriented in opposite directions around the perimeter of said toroid, and

a source of pulsed current connected to each said pair of coil windings.

5. Apparatus as defined in claim 1 wherein each said mode suppressor is L-shaped, one portion of said L passing through a respective aperture and extending from one broad Wall of said waveguide substantially to the other road wall thereof and another portion of said L extending toward a narrow wall of said waveguide.

6. Apparatus as defined in claim 1 wherein said apertures in said plate of gyrornagnetic material are rectangular in shape, the corners of the rectangular apertures adjacent said center arm having very sharp curvature.

References Cited UNITED STATES PATENTS 3,274,521 9/1966 Nourse 33324.1 3,277,401 10/1966 Stern 33324.1

FOREIGN PATENTS 671,206 4/ 1952 Great Britain.

HERMAN K. SAALBACH, Primary Examiner US. Cl. X.R. 

